1. Field of the Invention
The present invention relates to a process for producing glycidyl acrylate or glycidyl methacrylate (hereinafter sometimes collectively referred to as "glycidyl methacrylate, etc.") by reacting glycidol with methyl acrylate or methyl methacrylate (hereinafter sometimes collectively referred to as "methyl methacrylate, etc.") in the presence of a transesterification catalyst. Glycidyl methacrylate, etc. are widely used as starting raw materials for industrial use for resin modifieres, thermosetting coating materials, adhesives, textile treating agents, antistatic agents, ion exchange resins and the like.
In particular, glycidyl methacrylate, etc. with a minimized content of chlorine have recently been required in the fields of coating materials (especially powdery coating materials), electronic materials, textile materials and the like.
2. Description of the Related Arts
Glycidyl methacrylate, etc. are generally produced by a process in which acrylic acid or methacrylic acid is reacted with an alkali to form an alkali salt of acrylic acid or methacrylic acid, which is then reacted with epichlorohydrin in the presence of a quaternary ammonium salt, followed by dehydrochlorination.
The glycidyl methacrylate, etc. that are produced by the above-mentioned process usually contain residual chlorine compounds in an amount of about 1,000 to 10,000 ppm expressed in terms chlorine concentration. The aforesaid residual chlorine components not only bring about the deterioration of coating material properties, electrical properties and the problem of eruption on the skin in the fields of coating materials (for example, powdery coating materials), electronic materials, textile materials and the like but also involve a fear of carcinogenicity in recent years. Under such circumstances, it is required to improve the working environment where any of the above-mentioned materials is dealt with.
That is to say, the aforestated chlorine compounds contained as impurities are responsible for the deterioration of the performance of the resins themselves containing the glycidyl methacrylate, etc. and also the coating materials etc. as the purpose of use of the resins.
It is preferable therefore, that the chlorine compounds as impurities be removed as much as possible from the glycidyl methacrylate, etc. thus produced. However, the glycidyl methacrylate, etc. that are produced by the foregoing process usually contain residual chlorine components in an amount of several thousands ppm as chlorine, against which any effective method for removal is not proposed at all.
As a process for producing the glycidyl methacrylate, etc. free from a chlorine compound which process is different from the aforesaid process, there is available a process for producing the same by the transesterification of glycidol and methyl methacrylate, etc. It is thought that the glycidyl methacrylate, etc. produced by the transesterification is substantially free from a chlorine component, and is capable of greatly improving the deterioratin of amount of the of the resin modified therewith, toxicity thereof and environmental problems.
As a process for producing glycidyl methacrylate, etc. by the above-mentioned transesterification, there is disclosed, in Japanese Patent Publication No.38421/1972, a process in which the reaction is carried out in the presence of a phosphine as a catalyst. However, the amount of the production of glycidyl methacrylate as described therein is such that it was observed on the gas chromatograph, thereby making the process insignificant from the viewpoint of industrial production in general.
Japanese Patent Publication No.6133/1978 describes that the use of potassium cyanide as a catalyst enables the transesterification to proceed in a conversion of glycidol of 98%. Nevertheless, there are formed during the reaction, a Michael adduct of glycidol or methanol with methyl methacrylate or glycidyl methacrylate and an addition reaction product of a compound having an epoxy group such as glycidol and glycidyl methacrylate, and after the completion of the reaction, there is formed black to blackish brown precipitates in the form of solid or oil, which must be removed from the reaction system prior to the distillating purification of the glycidyl methacrylate, etc. The procedure not only complicates the production process but also lowers the purity of the objective product to be obtained by the regeneration of glycidol at the time of distillating glycidyl methacrylate, etc.
In addition, Japanese Patent Publication No.37268/1986 describes that glycidyl methacrylate is produced in a yield of 95% by synthesizing the same by the use of a strong alkali catalyst such as sodium methylate and immediately thereafter, removing the formed methanol under reduced pressure. However, the industrial use of such a catalyst is accompanied by considerable danger, since the catalyst must be filtered prior to the distillating purification of glycidyl methacrylate and in addition, a sodium alcoholate is generally an anion polymerization initiator for methacrylic acid esters.
On the other hand, Japanese Patent Application Laid-Open No.173783/1992 discloses in Comparative Example 3 of the specification, that glycidyl methacrylate is produced by dissolving potassium acetate as a catalyst in glycidol and adding the resultant solution dropwise in methyl methacrylate to cause the reaction. In the aforestated process, however, potassium acetate as a catalyst must be filtered after the completion of the reaction, and even if it is filtered, a slight amount of the catalyst thus dissolved causes the by-production of glycidol in the latter period of distillation for recovering glycidyl methacrylate, thereby markedly lowering the purity of the objective glycidlyl methacrylate.
Moreover, the use of patassium acetate as a catalyst suffers the disadvantage that it is necessary to provide a dissolving tank for dissolving potassium acetate in glycidol, while glycidol should be preserved at a low temperature, since it is made instable in the presence of potassium acetate.
Japanese Patent Application Laid-Open No.1780/1994 discloses in Example 1 of the specification, that glycidyl methacrylate is produced in high purity (98.9%) by a process in which triethylamine is employed as a catalyst, methanol which is formed by the reaction of glycidol and methyl methacrylate is rapidly distilled away by means of hexane, the conversion of glycidol is enhanced by the distillation while suppressing the formation of the adduct of methanol to methyl methacrylate and further suppressing the formation of glycidol in the latter period of the distillation.
Nevertheless, the above-disclosed process is disadvantageous in that it necessitates, in addition to glycidol and methyl methacrylate as principal staring raw material, hexane for removing methanol, thereby deteriorating the yield in a kettle; that it is required to carry out the purity regulation of methyl methacrylate to be recovered and reused, at every time of recovery because of hexane contained therein, thus complicating the procedure; that the amount of triethylamine contained in methyl methacrylate to be recovered and reused must be always checked, though it is explained that the triethylamine as a catalyst is removed at the time of recovering methyl methacrylate; and that a slight amount of amine is thought to be mixed in the objective glycidyl methacrylate, thereby decisively deteriorating the quality of the glycidyl methacrylate.
Although being independent of the transesterification catalyst according to the present, there are introduced quaternary ammonium salts and quaternary phosphonium salts as phase-transfer catalysts for the purpose of producing an alkyl cyanide by reacting sodium cyanide in a water layer with an alkyl halide in an oil layer. (Refer to Journal of the American Chemical Society, vol. 93, p. 195, Jan. 13, 1971.)